Chemical sensing and/or measuring devices and methods

ABSTRACT

Methods for fabricating silicon nanowire chemical sensing devices, devices thus obtained, and methods for utilizing devices for sensing and measuring chemical concentration of selected species in a fluid are described. Devices may comprise a metal-oxide-semiconductor field-effect transistor (MOSFET) structure.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 61/263,702, filed on Nov. 23, 2009 which is incorporated herein byreference in its entirety. The present application may be related toU.S. patent application Ser. No. 12/712,097 for ‘Methods for FabricatingHigh Aspect Ratio Probes and Deforming High Aspect Ratio Nanopillars andMicropillars’ filed on Feb. 24, 2010, U.S. patent application Ser. No.12/711,992 for ‘Methods for Fabrication of High Aspect RatioMicropillars and Nanopillars’ filed on Feb. 24, 2010, and U.S. patentapplication Ser. No. 12/822,109 for “Methods for Fabricating PassivatedSilicon Nanowires and Devices Thus Obtained,” filed on Jun. 23, 2010,the disclosures of all of which are also incorporated herein byreference in their entirety.

STATEMENT OF GOVERNMENT GRANT

The U.S. Government has certain rights in this invention pursuant toGrant No. HR0011-04-1-0054 awarded by Darpa, Grant No. W911NF-07-1-0277award by Army Research Office and Grant No. FA9550-04-1-0434 awarded bythe Air Force Office of Scientific Research.

FIELD

The present disclosure relates to silicon nanowire methods and/ordevices. Moreover in particular, it relates to chemical sensing and/ormeasuring devices and methods.

BACKGROUND

Defining high aspect ratio structures with controllable sidewalls insilicon has become increasingly important both in the nanometer andmicrometer scale for solar cells, microelectronic devices, and chemicalanalysis. High aspect ratio micrometer pillars can be used for solarcell investigations while nanometer scale high aspect ratio pillars canenable fundamental investigations in theories of nanopillar stressmechanics, silicon based lasers, and nanoscale electronic devices suchas finFETs and chemical sensors. Currently various nanofabricationtechniques exist that rely on self assembly or bottom-up processing.Some top-down processing enabling reproducibility in nanofabrication canalso be found.

Among further possible applications are mechanical oscillators andpiezo-resistive sensors. High aspect ratio nanopillars with diametersbetween 50-100 nm could prove useful for core-shell type plasmonicresonators while nanopillars with sub-10 nm diameters have shownpromising light emission characteristics.

SUMMARY

According to a first aspect, a device is provided, comprising: asemiconductor substrate with a planar surface; a semiconductornanopillar on the semiconductor substrate and substantiallyperpendicular to the planar surface; an insulating layer covering thesemiconductor nanopillar; a conductive layer covering the insulatinglayer, wherein the conductive layer and the insulating layer are devoidof an end portion thereof, thus exposing an uninsulated pillar end ofthe semiconductor nanopillar; and a functional layer covering theconductive layer.

According to a second aspect, a device is provided, comprising: asemiconductor substrate with a planar surface; a semiconductornanopillar on the semiconductor substrate and substantiallyperpendicular to the planar surface; an insulating layer covering thesemiconductor nanopillar wherein the insulating layer is devoid of anend portion thereof, thus exposing an uninsulated pillar end of thesemiconductor nanopillar; and a functional layer covering the insulatinglayer.

According to a third aspect, a method for fabricating a device isprovided, the method comprising: providing a semiconductor substratewith a planar surface; forming at least one semiconductor nanopillar onthe semiconductor substrate and substantially perpendicular to theplanar surface; covering the semiconductor nanopillar with an insulatinglayer; depositing a conductive layer on the insulating layer; covering aportion of the conductive layer with a masking layer; removing aconductive layer end of the conductive layer and an insulating layer endof the insulating layer, wherein the conductive layer end and theinsulating layer end are not covered by the masking layer, thus exposingan uninsulated pillar end; removing the masking layer; and forming achemical-attracting layer on the conductive layer, thechemical-attracting layer insulating the conductive layer.

Further embodiments of the present disclosure can be found in thewritten specification, drawings and claims of the present application.According to some embodiments of the present disclosure, the teachingsof the present disclosure provide a sensitive, selective, low-powerchemical sensor capable of operating reversibly and in real time todetect and measure concentration for chemical species such as ions andselected dissolved chemical species.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIGS. 1A-1F show fabrication steps of a device in accordance with anembodiment of the present disclosure. In particular:

FIG. 1A shows an exemplary semiconductor nanopillar (120) on asemiconductor substrate (110) with a planar surface (115)

FIG. 1B shows an exemplary insulating layer (130) covering thesemiconductor nanopillar (120) and substrate (110)

FIG. 1C shows an exemplary insulating layer (130) covered semiconductornanopillar (120) deposited with a conductive layer (140).

FIG. 1D shows an exemplary insulating layer (130) covered nanopillar(120) deposited with the conductive layer (140), wherein the conductivelayer (140) is coated with a masking layer (150).

FIG. 1E shows an exemplary insulating layer (130) covered nanopillar(120) deposited with the conductive layer (140) wherein an end portionof the nanopillar (120) is exposed forming an uninsulated pillar end(122).

FIG. 1F shows an exemplary insulating layer (130) covered nanopillar(120) deposited with the conductive layer (140) having the uninsulatedpillar end (122), and a functional layer (150) formed over theconductive layer.

FIG. 2 shows a cross-sectional view of an exemplary chemical sensingdevice in accordance with a further embodiment of the presentdisclosure.

FIG. 3 shows yet another exemplary chemical sensing device in accordancewith another embodiment of the present disclosure.

FIG. 4 shows a flow chart for an exemplary method for using the chemicalsensing device of the present disclosure for measuring chemicalconcentration.

DETAILED DESCRIPTION

In what follows, methods for fabrication of a chemical sensing deviceare described in accordance with various embodiments of the presentdisclosure. Nanoscale size pillars can be fabricated by way of exampleand not of limitation by: performing lithographic or self-assemblymethods to form mask followed by etching, use of lithography to patterncatalysts, and bottom-up techniques such as vapor-liquid-solid (VLS)growth. More details regarding fabrication techniques can be found incross referenced U.S. patent application Ser. No. 12/712,097 for‘Methods for Fabricating High Aspect Ratio Probes and Deforming HighAspect Ratio Nanopillars and Micropillars’ and U.S. patent applicationSer. No. 12/711,992 for ‘Methods for Fabrication of High Aspect RatioMicropillars and Nanopillars,’ both filed on Feb. 24, 2010, thedisclosures of which are incorporated herein by reference in theirentirety.

For clarity, the term ‘nanoscale’ is defined herein to be any structurebetween 1 nm and 500 nm in width. The term ‘pillar’ is defined as asubstantially upright shaft where the height is much greater than thewidth, e.g., 5-10 times greater than the width. The term “nanopillar” isdefined as nanoscale pillars.

Lithography is a process used in microscale fabrication to enableselective removal for parts of an underlying material by maskingportions which should remain. It uses light or electron beam to transfera geometric pattern from a photo mask to a light-sensitive or electronbeam sensitive chemical called a photoresist, coated on the underlyinglayer. The portion of the photoresist that is exposed to the light orelectron beam undergoes a chemical change which causes it to becomeeither soluble or insoluble in the developer solution compared to theunexposed portion depending on the tone of the resist (e.g., positive ornegative), thus leaving a mask of the desired pattern on the underlyingmaterial. The photoresist can be utilized as a mask directly for removalof exposed underlying material by a removal process such as reactive ionetch or be utilized to pattern a hard mask which can have betterresilience in more demanding removal or etching processes.

In accordance with an exemplary embodiment, the applicants utilized anelectron-beam type of photoresist to fabricate a patterned aluminumoxide (alumina) hard mask, then removed the electron-beam resist andutilized the patterned alumina hard mask during etching. Lithography andhighly anisotropic etching enables a routine fabrication of 30-50 nmnanopillars in silicon with over 40:1 aspect ratios. Transmission andscanning electron microscopy were used to characterize the nanopillarsat intermediate points in the process and for the completed pillars.

Subsequent oxidation can further define and enhance the nanopillars. Forexample, the nanopillars can be further reduced in diameter by asubsequent thermal oxidation, wherein the oxidation process can bedesigned to self-terminate by oxygen diffusion such that nanopillarsbelow 10 nm in width can be defined with wide processing latitude.Additionally, control of the oxidation process can produce siliconchannels which are strained for specific device applications.

Due to the nanometer dimensions and very high surface-to-volume ratios,the conductance of silicon nanopillars can depend strongly on surfacechemistry. For example, growing thermal oxide with or without gatemetals over a nanopillar creates a structure similar to traditionalMOSFETs where charges trapped at the oxide surface change the gatepotential which in turn controls the current flowing through thenanopillar core.

By functionalizing the oxide or gate surface, an array of siliconnanopillars can be converted into sensitive, selective, low-powerchemical sensors capable of operating reversibly and in real time todetect and measure chemicals such as ions and selected dissolvedchemical species. As an example, an oxide surface modified with3-aminopropyltriethoxysilane can act as a pH sensor, whereas a depositedgold electrode can adsorb hydrogen sulfide and detect H2S concentration.For non-specific ionic concentration, arrays of nanopillars can act aspoint probes for bulk conductivity measurements, while variably-spacednanopillars or fins can capacitively sense electric double-layer widthsand ionic screening effects without direct electrical connection to theenvironment.

Devices made from nanopillars are suitable for fabrication withinmicrofluidic channels, with geometries yielding low Reynolds numbers toensure laminar flow and proper device sensor operation. Features can beadded to devices to withstand harsh environment. For example, filterlayers may be defined by anisotropic dry etching and hermetically sealedby wafer bonding. With the anisotropic dry etching, it is also possibleto build robust filters with small filter openings that can be used toreduce the chance of mechanical damage to the nanopillars bymicro-particulates in suspension. By integrating additional featuressuch as one or more on-chip filters, on-chip Pt heaters, or electrolyticpressure generation systems, the device can operate with rapid unloadand reload fluid samples. This avoids limiting measurement speed bydiffusion of the sample, such as a chemical-containing fluid, to thedetector device, and enables the devices of the present disclosure tomeasure semi-continuously within changing environments

FIGS. 1A-1F show steps of fabricating a device for chemical sensing andmeasurement in accordance with the disclosure. The person skilled in theart will understand that the number of such steps is only indicative andthat the process can occur in more or fewer steps according to thevarious embodiments. For the sake of simplicity, throughout the presentdisclosure, the term ‘pillar’ intends to indicate semiconductornanoscale pillars or nanopillars.

FIG. 1A shows a cross-sectional view of a substantially verticalsemiconductor nanopillar (120) on a patterned, or etched semiconductorsubstrate (110) with a horizontally oriented planar surface (115). Byway of example and not of limitation, the substrate (110) and the pillar(120) are made of silicon (Si). The vertical semiconductor nanopillarscan also be fabricated on silicon-on-insulator (SOI) instead of bulksilicon substrate, or other semiconductor substrates such as GalliumArsenide or Germanium.

FIG. 1B shows a further cross-sectional view where the substrate (110)and the pillar (120) are covered by an insulating layer (130), e.g.,silicon dioxide (SiO₂) or other dielectrics. In case the pillar (120) ismade of silicon, the insulating layer (130) can be formed by oxidationor vapor phase deposition of silicon and oxygen containing species toform the insulating layer of silicon dioxide.

The terms “cover,” and its derivative forms “covered” “covering” and“coverage” are defined herein, for clarity, as completely covering allof the underlying material or materials (e.g., the insulating layercovering the pillar) unless specifically stated as otherwise (e.g.,covering portions of or selective coverage).

FIG. 1C shows a further cross-sectional view where the insulating layer(130) on the substrate (110) and the pillar (120) is covered by aconductive layer (140) of conductive material e.g., gold (Au) or silver(Ag). According to an embodiment of the disclosure, the conductivematerial can serve as electrostatic gate on an exterior perimeter and anend of the pillar (120) to modulate the conductivity of the pillar anddefines a conductive layer (140)-oxide (130)-semiconductor (120) (e.g.,MOS) structure. Such embodiment features a very low threshold voltage(e.g., on the order of 0.5 V) and high on/off ratio with lowsub-threshold slopes (e.g., less than 60 mV/decade), as the conductivelayer (140) can be deposited to surround the silicon nanopillar (120) onall sides, thereby enabling electrostatic control of a channel. A personskilled in the art of semiconductor fabrication will recognize anopportunity to integrate devices with very high density as a dimensionof a conducting channel inside the pillar (120) is nanometers in width.

FIG. 1D is a further cross-sectional view where a portion of theconductive layer (140) and the insulating layer (130) on a verticalportion of the pillar (120) is covered by a masking layer (155), whichcan be a photoresist or a hard mask. The masking layer (155) ispatterned so that it covers only selective portions of the pillar. Themasking layer (155) protects the covered portions of the conductivelayer (140) and the insulating layer (130) to allow selective removal ofthe conductive layer (140) and the insulating layer (130) in the nextstep.

FIG. 1E shows a further cross-sectional view where unprotected portionsof the insulating layer (131) and the conductive layer (141) from FIG.1D are removed from an end portion of the nanopillar (120), for exampleby a removal process such as etching or chemical-mechanical polishing(CMP). The conductive layer (140) and the insulating layer (130) on alower portion of the nanopillar (120) and a portion on the substrate(110) are not removed, as the masking layer (155) acts as a cover toprotect such portions from the removal process. After the removalprocess, the masking layer (155) is also removed.

The resulting structure shows, in FIG. 1E an uninsulated pillar end(122) and an insulating layer end (132) protruding beyond a conductivelayer end (142). The uninsulated pillar end (122) forms an electricallycontactable terminal. The uninsulated pillar end (122), the insulatinglayer end (132) and the conductive layer end (142) may or may notnecessarily terminate at the same location along the pillar. Accordingto an embodiment of the present disclosure, the uninsulated pillar end(122) should terminate at a height equal to or higher than theinsulating layer end (132) to ensure contact to the testing fluid.Additionally, the insulating layer end (132) should terminate at aheight equal to or higher on the pillar than the conductive layer end(122) to ensure proper insulation between the conductive layer (140) andthe electrically contactable terminal formed by the uninsulated pillarend (122). This distinction is for the embodiment of the presentdisclosure where the gate and the electrically contactable terminalformed by the uninsulated pillar end (122) are not tied togetherelectrically.

FIG. 1F shows a further cross-sectional view where the conductive layer(140) on the substrate (110) and the pillar (120) are covered by afunctional layer (150) which contains one or more chemical species whichcan attract and hold one or more selected types of chemical species suchas ions when a chemical-containing fluid (260) comes in contact to thedevice. Thus, the functional layer forms a chemically contactableterminal with the conductive layer (140). Therefore, the functionallayer (150) can also be known as a chemical-attracting layer (150). Theterms “functional layer” (150) and “chemical-attracting layer” (150) areused interchangeably herein.

In an embodiment of the present disclosure, the conductive layer (140)can be optional. The masking layer (155) is used to pattern theinsulating layer (130), and the functional layer (150) covers theinsulating layer (130). When chemical species, such as ions from thechemical-containing fluid (260) are attracted to and become trapped atthe functional layer surface, the chemical species act as gate to theFET.

The chemical-containing fluid (260) may be a gas, a liquid or asuspension. An example of the functional layer (150) can be3-aminopropyltriethoxysilane, which can attract hydrogen ions. Accordingto an embodiment of the present disclosure, the functional layer (150)can hold ions next to or near the conductive layer (140) and serve tomodulate an electrostatic gate formed by the conductive layer (140).

The functional layer (150) can be made of the same material as theconductive layer (140) and can be deposited at the same time. Forexample, gold material can be used to form a functional layer (150) forattracting H₂S and a conductive layer (140).

Another type of functional layer (150) can have fixed charges (e.g.,silicon dioxide, which cab have a partial negative charge on itssurface), so that electric double layer formation and ion screeningeffects can modulate the electrostatic gate terminal formed by theconductive layer (140). The modulation of ionic screening effect on theelectrostatic gate can vary as a function of interpillar distance andthus be used to sense specific chemical species such ions and measureion concentration.

According to various embodiments of the present disclosure and as shownin FIG. 1F, the functional layer (150) covers the conducting layer (140)and can insulate it from the chemical-containing fluid (260). Therefore,the functional layer (150) may physically encompass multiple materialsor layer to serve a dual function to attract chemical species and toinsulate. For example, for the functional layer (150) containing goldused to attract and sense H₂S, the functional layer (150) may be abilayer comprising an attractive layer (e.g., gold) covered by asemi-permeable layer which allows H₂S to pass through the semi-permeablelayer and reach the gold while insulating the underlying conductivelayer (140) and/or the attractive layer from the remaining chemicalspecies in the chemical-containing fluid (260). The constituentmaterials do not have to be physically separated by planar layers. Forexample, the functional layer (150) may also be an insulating,semi-permeable matrix with domains of gold within.

According to further embodiments of the present disclosure, the gateterminal can be tied to the electrically contactable terminal formed bythe uninsulated pillar end (122) and the functional layer (150) may nothave to insulate the conductive layer (140).

The formation of the functional layer (150) may be by deposition fromsolution, sputtering, vapor deposition, or other methods. Coverage ofthe functional layer (150) on the conductive layer (140) and not on theuninsulated pillar end (122) as shown in FIG. 1F can be provided by aselective deposition process which only deposits on the conductinglayer, or by an additional mask and removal process which removes thefunctional layer (150) from the uninsulated pillar end (122)

According to various embodiments in of the present disclosure, thedevice can be, but is not limited to, a variety of field-effecttransistors (FETs) such as a metal-oxide-semiconductor field-effecttransistor (MOSFET) to sense and measure chemical species.

FIG. 2 shows a cross-sectional view of an exemplary device in accordancewith a further embodiment of the present disclosure for sensing andmeasuring a chemical concentration of selected species. The substrate(110) and the uninsulated pillar end (122), contacted through achemical-containing fluid (260) (e.g., an ionic fluid), represent asource and a drain (or vice versa) of the device as a MOSFET for sensingand measuring ion concentration, while conductive layer (140) is thegate of the MOSFET chemical sensing device. The chemical-containingfluid (260) comprise of the selected chemical species and ion, wherebythe uninsulated pillar end (122) can be contacted through thechemical-containing fluid (260). However, the ions and the selectedchemical species may or may not be the same.

For example as shown in FIG. 2 the uninsulated pillar end (122) can be acurrent source and electrically contacted through thechemical-containing fluid (260) while the substrate can be a currentdrain terminal and electrically contacted through a backside contactlayer (270). The backside contact layer (270) can also be called abackside terminal. By forming a voltage difference between the sourceand drain, the current flow from the source to the drain is controlledby charges on or near the conductive layer (140) as the gate terminal.

Upon contacting the device to a chemical-containing fluid (260), theselected chemical species, in the chemical-containing fluid (260), canbe attracted by the functional layer (150) and change the amount oftotal charges on or near the conductive layer (140) gate. The change intotal charges on or near the conductive layer (140) gate terminalchanges the current flow from source to drain and can be used to sensethe presence of ions in the chemical-containing fluid. This would serveto modulate the current flow from the source to the drain. Suchconfiguration of the MOSFET structure, or a plurality thereof, can serveas the chemical sensing device.

For selected chemical species that are non-ionic, the total charge onthe gate terminal can changed by the displacement of fixed charges onthe functional layer (150). For example in case where the functionallayer (150) is gold, the gold surface can have a partial negative chargewhich can be removed when a selected chemical species such as H₂S isabsorbed on the gold surface.

FIG. 3 shows yet another exemplary chemical sensing device in accordancewith another embodiment of the present disclosure utilizing the chemicalsensing device to measure ion concentration or pH. Shown herein is aplurality of the pillars (120) fixed at an interpillar distance (385). Aconductive layer (140) is covered by a functional layer (150) having aplurality of fixed negative charges (352) on its surface.

A chemical-containing fluid (260) surrounding the pillars (120) providespositive ions which forms an electric double layer on each of the pillar(120) due to attraction to the fixed negative charges (352) of thefunctional layer (150). Positive charges of the electric double layer(380) on each of the pillars (120) can repel the positive charges on theelectric double layer (380) on its adjacent pillars (120), and thepositive charges in the chemical-containing fluid.

This repulsive force is greater at smaller interpillar distance (385)and can limit the amount of attracted charged ions (in this casepositive) from reaching the electric double layer (380). The repulsiveforce can also be moderated by the screening effect of the free ions inthe chemical-containing fluid (260) which shields the repulsive force ofthose adjacent the electric double layers (380).

Thus, an ion concentration model can be created for the net chargedensity of the double layer as a function of the interpillar distance(385) and the ion concentration of the chemical-containing fluid (260).By utilizing at least two chemical sensing devices, each with a distinctand known interpillar distance (385), the ion concentration of thechemical-containing fluid (260), can be measured by measuring the sourceto drain current flow for each of the two devices and comparing thedifference in the current flow to the difference between the interpillardistance (385) for the two devices.

FIG. 4 shows a flow chart for an exemplary method for using the chemicalsensing device of the present disclosure for measuring chemicalconcentration. The flow chart shows a method of measuring chemicalconcentration comprising: 1) providing the chemical sensing device(S410), 2) contacting a chemical-containing fluid (260) with the devicesuch that a selected type of chemical species in the chemical-containingfluid is suitable to be attracted by the functional layer (150) of thedevice (S420), 3) forming a voltage difference between the uninsulatedpillar end (122) and the semiconductor substrate (110) of the device(S430), and 4) measuring a change in current flow between one or more ofthe uninsulated pillar end (122) and the semiconductor substrate (110)of the device, thus measuring the chemical species concentration (S440).Although this embodiment shows a method comprising of four steps, it isnoted that the measurement can be accomplished in more or less steps.

In accordance with various embodiments of the present disclosure, theMOSFET structure has a functional layer (150) which can attract and holdselected chemical species from a chemical-containing fluid (260) next toor near the conducting layer (140) serving as a gate terminal for theMOSFET structure. As the movement of the chemical species in the fluidis in real time and the attraction of the functional layer (150) toselected chemical species can be designed to be reversible, theresulting device can function effectively as a real time, reversiblechemical sensor and chemical species measurement device.

The examples set forth above are provided to give those of ordinaryskill in the art a complete disclosure and description of how to makeand use the embodiments of the present disclosure, and are not intendedto limit the scope of what the inventors regard as their disclosure.Modifications of the above-described modes for carrying out thedisclosure may be used by persons of skill in the art, and are intendedto be within the scope of the following claims. All patents andpublications mentioned in the specification may be indicative of thelevels of skill of those skilled in the art to which the disclosurepertains. All references cited in this disclosure are incorporated byreference to the same extent as if each reference had been incorporatedby reference in its entirety individually.

It is to be understood that the disclosure is not limited to particularmethods or systems, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontent clearly dictates otherwise. The term “plurality” includes two ormore referents unless the content clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which the disclosure pertains.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the presentdisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

1. A device comprising: a semiconductor substrate with a planar surface;a semiconductor nanopillar on the semiconductor substrate andsubstantially perpendicular to the planar surface; an insulating layercovering the semiconductor nanopillar; a conductive layer covering theinsulating layer, wherein the conductive layer and the insulating layerare devoid of an end portion thereof, thus exposing an uninsulatedpillar end of the semiconductor nanopillar; and a functional layercovering the conductive layer.
 2. The device of claim 1, wherein theuninsulated pillar end forms an electrically contactable terminal andthe functional layer forms a chemically contactable terminal.
 3. Thedevice of claim 1, wherein the functional layer is configured to attracta selected type of chemical species.
 4. The device of claim 1, whereinthe functional layer is configured to attract ions.
 5. The device ofclaim 1, wherein the functional layer is a bilayer, the bilayercomprising: an attractive layer for attracting a selected type ofchemical species; and a semi-permeable insulating layer, thesemi-permeable insulating layer being on the attractive layer, whereinthe semi-permeable insulating layer is configured to allow the selectedtype of chemical species to pass through and to insulate the attractivelayer and the conductive layer of the device.
 6. The device of claim 1,wherein the semiconductor nanopillar and the semiconductor substrate aremade of silicon.
 7. The device of claim 1, further comprising aconductive backside terminal coated on a backside of the semiconductorsubstrate, opposite the semiconductor nanopillar.
 8. The device of claim7, the device being a metal-oxide-semiconductor field-effect transistor(MOSFET) structure.
 9. The device of claim 8, the conductive layer beinga gate terminal of the MOSFET.
 10. A microfluidic channel structurecomprising one or more devices according to claim
 1. 11. The device ofclaim 1, wherein the semiconductor nanopillar is a plurality ofsemiconductor nanopillars.
 12. The device of claim 9, wherein thesemiconductor substrate is a source or a drain of the MOSFET and theuninsulated pillar end is respectively the drain or the source of theMOSFET.
 13. A device comprising: a semiconductor substrate with a planarsurface; a semiconductor nanopillar on the semiconductor substrate andsubstantially perpendicular to the planar surface; an insulating layercovering the semiconductor nanopillar wherein the insulating layer isdevoid of an end portion thereof, thus exposing an uninsulated pillarend of the semiconductor nanopillar; and a functional layer covering theinsulating layer.
 14. A method for fabricating a device, the methodcomprising: providing a semiconductor substrate with a planar surface;forming at least one semiconductor nanopillar on the semiconductorsubstrate and substantially perpendicular to the planar surface;covering the semiconductor nanopillar with an insulating layer;depositing a conductive layer on the insulating layer; covering aportion of the conductive layer with a masking layer; removing aconductive layer end of the conductive layer and an insulating layer endof the insulating layer, wherein the conductive layer end and theinsulating layer end are not covered by the masking layer, thus exposingan uninsulated pillar end; removing the masking layer; and forming achemical-attracting layer on the conductive layer, thechemical-attracting layer insulating the conductive layer.
 15. Themethod of claim 13, wherein the uninsulated pillar end forms anelectrically contactable terminal and the chemical-attracting layerforms a chemically contactable terminal.
 16. The method of claim 13,wherein the chemical-attracting layer is configured to attract aselected type of chemical species.
 17. The method of claim 13, whereinthe chemical-attracting layer is configured to attract ions.
 18. Themethod of claim 13, wherein forming the chemical-attracting layerincludes: forming an attractive layer for attracting a selected type ofchemical species; and forming a semi-permeable insulating layer on theattractive layer wherein the semi-permeable insulating layer isconfigured to allow a selected type of chemical species to pass throughand to insulate the attractive layer and the conductive layer of thedevice.
 19. The method of claim 13, wherein the semiconductor nanopillarand the semiconductor substrate are made of silicon.
 20. The method ofclaim 13, further comprising coating a backside terminal on thesemiconductor substrate on a side opposite the nanopillar.
 21. Themethod of claim 19, wherein the device forms a metal-oxide-semiconductorfield-effect transistor (MOSFET) structure.
 22. The method of claim 20,wherein the conductive layer forms a gate terminal of the MOSFET. 23.The method of claim 21, wherein the semiconductor substrate forms asource or a drain of the MOSFET and the uninsulated pillar end formsrespectively the drain or the source of the MOSFET.
 24. The method ofclaim 14, wherein fabricating the device includes fabrication within oneor more microfluidic channel structures.
 25. The method of claim 14,wherein the semiconductor nanopillar is a plurality of semiconductornanopillars
 26. A method of measuring chemical species concentrationcomprising: providing the device according to claim 1; contacting achemical-containing fluid with the device such that a selected type ofchemical species in the chemical-containing fluid is suitable to beattracted by the chemical-attracting layer of the device; forming avoltage difference between the uninsulated pillar end and thesemiconductor substrate of the device; and measuring a change in currentflow between one or more of the uninsulated pillar end and thesemiconductor substrate of the device, thus measuring the chemicalspecies concentration.
 27. The method of claim 26, wherein forming thevoltage difference includes contacting the uninsulated pillar end withthe chemical-containing fluid.
 28. The method of claim 26, wherein thedevice is a first device, the method further comprising: providing asecond device; measuring a change in current flow between theuninsulated pillar end and the semiconductor substrate of the seconddevice; obtaining a difference between the change in current flow(between the uninsulated pillar end and the semiconductor substrate) ofthe first device and the change in current flow (between the uninsulatedpillar end and the semiconductor substrate) of the second device; andcomparing the difference to an ion-concentration model thus measuringthe ion concentration.
 29. The method of claim 27, wherein the firstdevice comprises a plurality of pillars with a first interpillardistance and the second device comprises a plurality of pillars with asecond interpillar distance different from the first interpillardistance.
 30. The method of claim 26, wherein the device furthercomprising a plurality of semiconductor nanopillars.
 31. The method ofclaim 26, wherein the device is within a microfluidic channel structure.